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Full text of "The manufacture and properties of iron and steel"

THE BASIC-BESSEMER PROCESS.                            121
ganese the rephosphorization is less, but with bad practice it may be a troublesome factor. In "pig-iron No. 2," Table VII-A, the silicon is low in the pig, and the slag is rich in bases, yet the phosphorus in the metal was raised from .061 to .084 per cent., giving a content too high for the softest grades. The records in these tables relate to general practice some years ago, and can hardly be said to represent the best work to-day, Rephosphorization is now controlled by keeping the temperature as low as possible, by using a calcareous cinder, and by preventing the mixing of slag and steel during recarburization. This is done by decanting the slag before pouring the steel, and making a dam to hold back the remainder of the cinder. In going over the records of one of the best works in Germany and taking averages of large numbers of heats, the rephosphorization in rail steel was about .025 per cent. Five averages resulted thus, in each case the first figure being the bath before recarburization and the second the final steel: .044 to .070; .039 to ,056; .036 to .062; .032 to .056; .043 to .070. In no case was there any charge where the resultant phosphorus was beyond the usual limit for rails. In soft steels the rephosphorization is less, owing to the less violent reaction, and the phosphorus content is lower than just shown in rail steel, but the variations, both in phosphorus and sulphur, are greater than in American open-hearth steel. The established American standards call for below .04 phosphorus in all basic steel for bridges and boilers, and every heat is analyzed for sulphur, something that is seldom done on the Continent. The foreign engineers are in no degree so exacting as the American in regard to chemical composition.
Note:  Further remarks on the operation of basic converters will be found in Chapter XXIV.